The geological record shows that, although the Earth's crust was very thin and hot during the Proterozoic, mountains were still able to form thanks to the deformation forces of the extinct crust.
The geochemical and geological records provide very important key insights into the tectonic history of the Earth, but in terms of the formation of mountains during the Proterozoic.
The Proterozoic is a period that represents a period before the emergence of the first complex life on Earth. This period lasted from 2500 to 542 million years ago and was previously part of the Precambrian period.
In the geochemical records found, there are things that contradict each other. First, geochemical evidence suggests that the Earth at that time had a thin, hot crust, which generally indicates that mountains would not have been able to form. On the other hand, there are rocks left behind from that time period that indicate the existence of a mountain.
"So how do we combine conflicting geological evidence for mountain formation with geochemical evidence of thin crust?" asked Christopher Spencer, a geologist at Queen's University in Ontario, Canada, quoted from EOS.org.
Using a global database, Spencer compared the rock record with the geochemical record from 1.8 billion to 850 million years ago, a period that began about a billion and a half years after the earliest signs of life, and ended 150 million years before complex life evolved.
The geochemistry of continental rocks has since shown that the continental crust was thin (less than 40 kilometers), and was subjected to extremely poor heat conditions to form mountains.
Despite the hot crust, the mineral composition of rocks from around the world at that time indicates that there was a significant crustal flow that resulted in the lower mountains.
"The process of building mountains under these unique conditions is something we have never seen on modern Earth or beyond. Mountains during the Proterozoic were different from mountains at any other time in Earth's history," Spencer said.
The study's authors argue that, with the crust being thin and hot, mountains could still form because the relatively weak crust slides past itself in collisions that are more like fleeting blows, rather than head-on collisions.
That behavior is partly due to the hot bottom of the crust "flowing" like a highly viscous fluid on geological timescales, even before modern plate tectonics began.
This account of extinct plate tectonic forces brings together geological and geochemical evidence, describing a relatively flat Earth that lasted for a billion years. Flat is meant here is because the mountains have not been formed towering like now.
"Continental movement is possible without global plate tectonics," said Taras Gerya, a geophysicist from the Swiss Federal Institute of Technology (ETH Zurich) who was not involved in the study.
